An object to perform a surface treatment on the surface of a display is to improve image contrast by improving the abrasion resistance of the display and decreasing the reflection of light emitted from an external light source. The decrease of the reflection of external light can be achieved by two methods. One method causes diffused reflection by using convexo-concave shape on the surface, and the other method causes destructive interference by using a multi-coating design.
Anti-glare coating using the convexo-concave shape on the surface has been generally used in the related art. However, there have been problems in that resolution deteriorates in a high-resolution display and the sharpness of an image deteriorates due to diffused reflection. In order to solve the above-mentioned problems, Japanese Patent Application Publication No. 11-138712 has disclosed a light-diffusion film where light is diffused in a film that is manufactured by using organic filler having a refractive index different from a binder. However, since having been problems in that luminance and contrast deteriorate, the light-diffusion film needs to be modified.
A method of causing the destructive interference of reflected light by a multi-coating design has been disclosed in Japanese Patent Application Publication Nos. 02-234101 and 06-18704. According to this method, it is possible to obtain antireflection characteristic without the distortion of an image. In this case, light reflected from layers should have phase difference in order to allow reflected light to destructively interfere, and a waveform of reflected light should have amplitude so that reflectance can be minimized reflectance during the destructive interference. For example, when an incidence angle with respect to a single antireflection coating layer provided on the substrate is 0°, the following expressions can be obtained.nons=n12 2n1d1=(m+½)λ (m=0, 1, 2, 3 . . . )  [Math FIG. 1](no: the refractive index of air, ns: the refractive index of a substrate, n1: the refractive index of a film, d1: the thickness of the film, λ: the wavelength of incident light)
In general, if the refractive index of the antireflection coating layer is smaller than the refractive index of the substrate, antireflection is effective. However, in consideration of the abrasion resistance of the coating layer, it is preferable that the refractive index of the antireflection coating layer is 1.3 to 1.5 times of the refractive index of the substrate. In this case, the reflectance is smaller than 3%. However, when an antireflection coating layer is formed on a plastic film, it is not possible to satisfy the abrasion resistance of a display. For this reason, a hard coating layer of several microns needs to be provided below the antireflection coating layer. That is, the antireflection coating layer using the destructive interference includes a hard coating layer for reinforcing abrasion resistance, and one to four antireflection coating layers that are formed on the hard coating layer. Accordingly, the multi-coating method obtains antireflection characteristic without the distortion of an image. However, there is still a problem in that manufacturing cost is increased due to the multi-coating.
A method of allowing reflected light to destructively interfere by a single coating design has been proposed in recent years. The following method has been disclosed in Japanese Patent Application Publication No. 07-168006. According to the method, ultrafine particle dispersed liquid is applied on a substrate, and the spherical shapes of fine particles are exposed to the surface so that the difference in refractive index is gradually generated between air (interface) and the particle. As a result, it is possible to obtain antireflection characteristic. However, since the shape and size of the ultrafine particles should be uniform and these particles should be uniformly distributed on the substrate, it is difficult to achieve this method by general coating processes. Further, since the amount of a binder should be equal to or smaller than a predetermined amount in order to obtain a spherical shape on the surface of the film, there is a problem in that this method is very vulnerable to abrasion resistance. Further, since the coating thickness should be also smaller than the diameter of the fine particle, there is a problem in that it is very difficult to obtain abrasion resistance.